One safety feature introduced in many new road and highway constructions is the inclusion of sonic noise (or nap) alert patterns (SNAPs) created as rumble strips alongside driving lanes. These depression patterns interfere with the smooth driving of a vehicle by creating a noise and a vibration when a vehicle encounters the pattern. This interference serves as a warning to drivers that they are leaving the desired driving lane, for example due to a lapse in attention or drift. Once warned, the driver can preferably correct the vehicle's course, if leaving was unintentional or inadvertent.
There have been various methods for imparting the depression patterns to the roadway asphalt or concrete. One method has been to apply a roller with protrusions matching the desired pattern while the asphalt is still hot and/or the concrete is still wet. This method does not work after the material has set. An alternate method involves plunge grinding depressions by mechanically raising and lowering a grinding drum in each position where a depression is desired. This can be a lengthy process and requires precise re-positioning for each new cut. A still further method, as discussed in U.S. Pat. No. 5,391,017, utilizes an offset axle on a front bearing wheel or an elliptical wheel to raise and lower the entire grinding machine as the wheel rotates. On less than ideal surfaces, the bearing wheel can slip, causing poor depression spacing.
Consequently, there is a need for an improved grinding machine to create depression patterns along roads.